In this work, the Diels-Alder reaction between the acrylate groups of acrylated epoxidized soybean oil and the furan rings of p-tertiary butyl phenol furfural resin (TBPF) is described. The reaction was carried out at 110 degrees C in presence of FeCl(3) catalyst, and tough polymers were obtained in 1 h. Surprisingly, samples that were heated and cooled 5, 10, and 20 times to 140 degrees C and room temperature had better mechanical properties than samples that were kept at 140 degrees C for the same total duration. This unexpected behavior is attributed to a series of forward and retro Diels Alder reactions between the functional groups. To prove this hypothesis, a model reaction between TBPF and n-butyl acrylate was studied. At 100 degrees C, (1)H-nuclear magnetic resonance signals of the furan ring protons disappeared, only to reappear at 140 degrees C. Thermogravimetric analysis of the adduct showed a weight loss at 140-150 degrees C, which was in quantitative agreement with the amount of butyl acrylate. Infrared analysis showed that furan rings were not completely consumed by extended heating at 110 degrees C. After five heating and cooling cycles of much shorter duration at 140 degrees C, the furan absorption in the infrared disappeared. The storage modulus of acrylated epoxidized soybean oil-TBPF samples after 20 heating cycles was 1.15 GPa. (C) 2010 Wiley Periodicals, Inc. J Appl! Polym Sci 120: 1707-1712, 2011